Many past health coverage expansions experienced low participation levels by the uninsured who qualified for help. To avoid similar pitfalls with national health reform, policymakers need to incorporate 21st-century approaches to eligibility determination, enrollment, and retention. One such approach qualifies individuals for subsidies based on reliable data in government hands rather than consumers' completion of traditional application forms. Federal income tax data could thus establish eligibility for subsidies, since more than 6 out of 7 uninsured-86.3 percentfile such returns. Such data-driven eligibility may also lower administrative costs and error rates.